A study published in the BMJ has linked poor growth in the first 3 months (the first trimester) of pregnancy with poor heart health later in life.

The rate of human development is highest during the first trimester of pregnancy, and this is when the cardiovascular and metabolic organs form.

The growth of the fetus in this time is influenced by many factors, including the age of the mother and whether she smokes, ethnicity and blood pressure. Various health problems can be indicated by the size of a fetus during its first trimester.

Although studies have previously found a link between low birth weight and risk of heart problems, researchers have not known until now whether there is a link between small size in the first trimester and heart disease later in life.

Risk factors for heart disease

Researchers in the Netherlands studied 1,184 children, dividing them into groups based on the size they had been during the first trimester of pregnancy.

At the age of 6, the children were examined for risk factors for heart disease. This involved checking the body mass index (BMI), body fat distribution, blood pressure, cholesterol levels and insulin concentrations of the children.

Children who were small in the first trimester of pregnancy had more risk factors for heart disease at age 6.

The researchers found that the children who had been the smallest as fetuses had significantly greater risk factors for heart disease than children who had been larger as fetuses in the first trimester. The children who had been smaller in the first trimester had greater fat mass and higher blood pressure and cholesterol.

Low birth weight and small size in early pregnancy are not the cause of future heart problems in themselves, but they are symptoms of factors that adversely affect fetal development during pregnancy.

Scientists still do not know much about how problems affecting fetal growth can lead to heart disease, so more ultrasound studies looking at the first trimester are needed.

The study's authors say that, although heart disease may partly originate in factors influencing first trimester development, there could also be contributing factors from the mother in the pre-conception period, such as undernutrition, anemia or smoking.

More studies are needed to confirm the findings

Although this study shows that the first trimester is an important period for cardiovascular and metabolic development, it is important to remember that a fetus that is small in the first trimester will not necessarily grow to have heart problems in later life. In fact, the risk factors that the researchers observed in the 6-year-old children were small, and none of the children had heart disease.

The authors of the study acknowledge that some of their results may have arisen by chance. In the study's conclusion, the researchers state that "the large number of statistical tests that we did may have led to false positive associations."

And some of the pregnancies may have been incorrectly classified, because it was difficult to be accurate about how old the fetuses were when they were measured.

"This is a very specific study, the first from early pregnancy onwards. We could only include a relatively small number of subjects from a large study. We will perform follow-up studies to replicate these findings and the underlying mechanism in other study groups."

More research needs to be done before the biological reasons for this link between fetal size in the first trimester and risk of cardiovascular disease can be understood. The researchers also do not yet know what the long-term consequences may be.

"We need a deeper understanding of the strength, nature and mechanisms of the reported associations before rushing to intervene," the authors conclude.

First trimester is a 'critical stage' in baby development

The British Heart Foundation (BHF) have also issued a statement on the study's findings:

"The first few months of pregnancy are a critical stage in a baby's development, and this study suggests that fetal growth within this time may influence their heart health later in life.

However, as the researchers acknowledge themselves, further studies are needed to understand why this pattern exists and what it might mean for preventing heart disease."

The BHF recommend that "if you are pregnant, or planning a family, you should be thinking about your baby's heart health as well as your own." This includes taking steps to quit smoking, for women who smoke, and keeping a check on blood pressure.

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